The close-knit water polo community has continued to grieve the loss of USC freshman Jon Walters, a Newport Beach resident who died Wednesday afternoon at Santa Ana's Western Medical Center at the age of 19.

Bill Walters told the Orange County Register that his son died of a heart attack. Lt. Jeff Hallock of the Orange County Sheriff's Department said Thursday that an unresponsive Jon Walters was admitted to Chapman Medical Center in Orange on Jan. 1.

Walters was moved to Western Medical Center a few days later. He died there at 3:35 p.m. Wednesday, according to records from the sheriff's Orange County Coroner Division.

No official cause of death had been released as of Thursday evening.

"We're still waiting for the doctor to sign the death certificate," Hallock said Thursday. "Hypothetically, if the doctor doesn't feel comfortable signing it, they'd do an autopsy."

The OC Coroner Division is investigating the death and an autopsy will be scheduled to help determine the cause of death, according to the organization’s website.

A memorial service for Walters is planned for 11 a.m. Jan. 18 in the community center of Mariners Church in Irvine.

Walters, a center, played at Newport Harbor High his freshman year before transferring to Mater Dei. The CIF ruled him ineligible for his sophomore season, but he came back to help the Monarchs win two CIF Southern Section 1 titles. Mater Dei went undefeated both years, part of a CIF record 105-game winning streak that ended in November.

Walters was one of the best and most well-known boys' water polo players to come out of Orange County in recent years. In his senior year, 2012-13, he was named the Division 1 and Orange County Player of the Year after the Monarchs won their third straight Division 1 title. In his freshman year at USC, he overcame an elbow injury to score 17 goals, helping the Trojans win their sixth straight national title.

Paul Fink, whose son Curtis grew up playing club water polo with Jon Walters and later against him in high school for Newport Harbor, knew Walters well from a young age.

"He was a champion," Paul Fink said. "What's so sad is that he had such a bright future, not only in academics, but he was a future Olympian. He was a contributor [for USC as a freshman]. He wasn't just a kid on the team. He had an impact for them, made a difference for them. But he's been that way everywhere he went, since 10-and-under and 12-and-under water polo.

"The neat thing for me as a parent, being able to watch that, was that he made the kids around him better. When he was younger, every single kind wanted to be Jon. He would go in there and dominate the pool, and afterward he had a smile on his face. What kid didn't look up to that and want him on their team?

"The whole sport of water polo was better for having kids like him. They'd see him with a medal around his neck or a trophy in his hand, and a smile on his face, and every kid wanted to be that.... You could never hate him for winning, because he played with such a great deal of charisma."

Newport Harbor boys' water polo coach Robert Lynn said he agreed with the assertion that Walters could have been on the Olympic path.

"I liked Jon very much," said Lynn, a 2000 Olympian who was an assistant coach for Team USA in 2008 and 2012. "He played for me in the Junior World Championships, and he was a stud. It's just a tragedy. We just watched him play in NCAA Finals, and I knew him personally. He was a great kid. He was a strong workhorse."

Walters is survived by his father and mother, Jacque, as well as four siblings. His older sister Ali was a standout tennis player at Corona del Mar High and later Pepperdine. Jon's younger brother, James, was a senior captain this year for Mater Dei boys' water polo and also is headed to USC.

Walters seemed to have a magnetic personality. His friend Chloe Glore, who played water polo at Newport Harbor before graduating last year, posted a picture on Twitter of the two of them together.

Glore said she had known Walters for about 10 years, since she and her older brother Garret played club water polo at club Split OC. Twice, she said, she took him to the winter formal dance. Glore said she last heard from Walters just before Christmas, when he sent her a text message saying that he loved her.

"He was honestly the nicest person I've ever met," Glore said. "He was super easygoing, super funny. He was just a really genuine person ... he had a lot more to do in his life."

Others also took to social media to express their feelings. Newport Harbor High alumna Kaleigh Gilchrist, who helped USC women's water polo win a national title last spring, posted on Twitter: "Rest in paradise to one amazing guy. We love you Jon Walters."

And Chase Watson, the Corona del Mar High product who was Jon Walters' teammate at USC, posted on Facebook: "Rest in peace Jon. Love you forever and see you on the other side. We lost a great one in you."

Lynn said that Walters was just a rare athlete.

"All of Newport sends its condolences to the family," Lynn said. "All of Newport is traumatized by this, to tell you the truth. You know what they say, someone must have needed him up there, because he was a good soldier and a good person."

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